Temperature sensing device

ABSTRACT

A conductive heat transfer mechanism through which energy readily flows between two bodies or systems at different temperatures. The present mechanism is embodied in a temperature sensing network for determining and controlling the surface temperature of a xerographic fuser roll. The network includes a probe shoe containing at least one temperature sensing element with the shoe being positioned in close non-contiguous relation with the moving surface of a heated fuser roll. A magnetic flux field is created within the air gap between the heated roll surface and the probe shoe and a magnetic medium, preferably being in fluid form, having a relatively high coefficient of thermal conductivity is placed within the flux field through which a rapid and efficient flow of heat is maintained.

United States Patent [191 Thettu June 10, 1975 TEMPERATURE SENSINGDEVICE Primary Examiner-John J. Camby [75] Inventor: Raghulinga R.Thettu, Webster,

NY. [57] ABSTRACT 73 Assignee; Xerox Corporation, St f d A conductiveheat transfer mechanism through which Conn. energy readily flows betweentwo bodies or systems at different temperatures. The present mechanismis em- [22] Flled: 1973 bodied in a temperature sensing network fordetermin- [21] Appl. No.: 388,676 ing and controlling the surfacetemperature of a xerographic fuser roll. The network includes a probeshoe containing at least one temperature sensing element [52] US. Cl.432/36; 73/351; 432/60 i h h being positioned in cluse non contiguuus [5i Ilil. Cl. F27!) 9/24 relation with the moving Surface of a heatedfuser to [58] Fleld 0' Search 432/36, 60; 73/35l A magnetic flux field icreated within the air gap tween the heated roll surface and the probeshoe and [56] References and a magnetic medium, preferably being influid form,

UNITED STATES PATENTS having a relatively high coefficient of thermalconduc- 3,357,249 12/1967 Bernous et al 73/351 ti y is placed i n the flx fi l th ug which a 3,690,!76 9/1972 Connolly 73/35! rapid andefficient flow of heat is maintained. 3,8135 I6 5/!974 Kudsi et al .7432/60 4 Claims, 4 Drawing Figures PATENTEDJIJN 1 0 SHEET 2 TEMPERATURESENSING DEVICE This invention relates generally to a heat transferdevice and, in particular, to apparatus for sensing the surfacetemperature of a fuser roll as conventionally utilized in thexerographic copying art.

Heretofore, most heat transfer systems for determing the temperature ofa given body have been of the contact type wherein the sensing elementis placed in direct physical contact with the body under investigation.In order to get a truly responsive sampling of the surface temperature,the probe should preferably encompass as much of the heated surface areaas is practically possible, Maintaining the positive contact requiredfor uniform and efficient heat flow between the two contacting surfacesover a large area has been difficult to accomplish particularly in thecase where the heated surface is rough, irregular or arcuate in shape.When the heated surface under investigation is moving, as for example,as in the case of a moving heated pressure roll surface asconventionally utilized in the xero' graphic process, a good deal ofsurface resistance is also developed between the surface which leads toerroneous temperature information being transmitted therebetween.Similarly, a dissimilar temperature reading is normally generated forthe same body temperature when the heated body is held in a stationarycondition then when it is moving. Likewise, any contaminants such asdirt, toner, lint or the like coming between the contacting probesurface and that of the body under investigation further aggravates allof the problems herein alluded to. In short, it has heretofore beenextremely difficult, if not impossible, to maintain an accurate flow ofthermal information between two contacting surfaces.

It is therefore an object of the present invention to provide a mediathrough which heat energy can be rapidly and efficiently transferredbetween two bodies regardless of the shape of the body or whether or notone of the bodies is in motion.

A further object of the present invention is to improve heat pressureroll image fixing systems.

Another object of the present invention is to provide a reliablemechanism for sensing the surface temperature of a heated pressure roll.

A still further object of the present invention is to control the inputenergy provided to a heated pressure roll in order to produce a uniformsurface temperature at the roll surface under varied operatingconditions.

Another object of the present invention is to reduce the contactresistance generated between a temperature sensing probe and a heatedpressure roll surface.

These and other objects of the present invention are attained by meansof a temperature sensing device arranged to provide information to afuser control network, the sensor including a sensing probe shoe forsupporting a sensing element and being positioned in closenon-contiguous proximity with the surface of a heated pressure roll. Amagnet is positioned adjacent to the probe shoe, preferably behind theprobe surface, which is capable of establishing a flux field directed atthe roll surface. A magnetic fluid having a low surface energy isintroduced into the magnetic flux field to provide a thermal circuitbetween the roll surface and the sensing probe element which exhibits alow contact resistance in regard to the fuser roll surface through whichenergy is conductively transferred from the roll to the sensor.

For a better understanding of the invention as well as other objects andfurther features thereof reference is had to the following detaileddescription of the present invention to be read in connection with theaccompanying drawings, wherein:

FIG. 1 is a schematic elevation of an automatic xerographic copyingmachine utilizing the teachings of the present invention;

FIG. 2 is an enlarged sectional view illustrating a pressure roll heatfixing system utilized in the auto matic copying machine shown in FIG. 1showing the sensing probe mounted in close proximity to the fuser rollsurface;

FIG. 3 is an enlarged partial view of the probe shoe of the sensingelement illustrating the conforming characteristics of the magneticfluid positioned between the shoe and the fuser roll surface;

FIG. 4 is a diagramatic illustration of one embodiment of the magneticarrangement utilized in the present invention.

Referring now to FIG. 1, there is illustrated a schematic representationof an automatic xerographic reproducing machine employing thetemperature sensing device of the present invention. It should be notedthat the apparatus of the present invention will be explained inconjunction with the reusable xerographic process. However, it should beclear to one skilled in the art that the apparatus of the presentinvention is not so limited and that the invention has wider applicationin any environment where it is desirous or necessary to accuratelyascertain the surface temperature of a heated body.

Because the xerographic copying process is well known and used in theart, the processing steps herein employed will only be briefly describedin reference to FIG. 1. Basically, the heart of the machine involves aphotosensitive plate 10 which is formed in a drum configuration. Thedrum is mounted upon a horizontally aligned support shaft 12 and causedto rotate in the direction indicated so that the photosensitive platepasses sequentially through a series of processing stations. The drumshaped plate basically consists of an outer layer 13 of photoconductivematerial, such as selenium or the like that is placed over a groundedsubstrate 14.

In operation, the plate is initially charged to a uniform potential at acharging station A by means of a corona generator 15. The uniformlycharged plate surface is then moved into an imaging station B wherein aflowing light image of the original document, which is supported upon aviewing platen 17 is projected onto the photoconductive plate surface bymeans of a moving scanning lens element 18 and a pair of mirrors 19 and20. As a result of the imaging process a latent electrostatic imagecontaining the original subject matter is recorded on thephotoconductive plate surface.

The latent image is next transported on the drum through a developingstation C wherein the latent image is rendered visible by theapplication of specially prepared charge toner particles which arecascaded over the image plate surface. The now visible toner image isthen transported into the next subsequent processing station, an imagetransfer station D, wherein a sheet of final support material is fedfrom either one of two supply tray areas, an upper supply tray 24 and alower supply tray 25, via sheet registering and forwarding mechanism 30in synchronous moving contact with the visible image carried on theplate surface. The support sheet and the charged toner image on the drumsurface are moved together under a transfer corona generator 27 whichserves to electrostatically transfer the toner images in imageconfiguration from the drum surface onto the contacting side of thesupport sheet. The imaged sheet is then stripped from the drum surfaceby means of a pick offfinger 28 and directed along a stationary vacuumtransport 29 into the nip ofa heat pressure roll system F. For furtherdetails concerning this type of fusing device, reference is had to US.Pat. NO. 3,498,586 which issued in the name of Moser.

As noted above, the automatic copying device has the capability ofproducing either single sided copy, that is copy bearing a toner imageon one side thereof or double sided copy. In a single sided mode ofoperation, the final support sheets are fed from either one of the twosupply trays directly into the image transfer station via the sheetforwarding and registering mechanism 30. Upon the accomplishment of thetransfer step, the image sheet is passed through the fuser roll assemblyand forwarded directly into a copying tray 29 where the copies arestored and held until such time as the machine operator removes them. Onthe other hand, when a two sided copying mode of operation is selected,movable transport 26 within the circular paper path, is lowered to thedotted line position as shown in FIG. 1 and the upper supply tray, whichhas previously been emptied of all support material is automaticallyprepared to accept a copy sheet directed therein. The copy sheets arethen fed from the lower support tray to the image transfer station andthe image fusing station directly into the upper support tray area wherethe sheets are stored until the machine is further programmed for asecond run. Upon the initialization of the second copy run, the movabletransport 26 is once again raised to solid line position as shown inFIG. 1 and the once imaged copy sheets are fed again directly from theupper supply tray through the transfer and fusing stations wherein asecond image is created on the opposite or previously non-image side ofthe sheet. After fusing, the two sided copy sheets are fed directly intoa copy tray in the manner herein described above.

Referring now more specifically to FIGS. 2-4 there is shown a preferredembodiment of the subject invention in a suitable environment such asthat disclosed in the above noted patent to Moser. The preferredembodiment of the present invention includes two temper ature responsiveresistance elements 40 and 41 which can be of any commerically availabletype such as those supplied by Victor Engineering of Springfield, NewJersey. However. it should be clear that the invention is not limited tothis specific type or number of sensing elements and any suitable sensorcapable of producing either an ampere change or voltage change inresponse to a change in temperature sensed can be utilized hereinwithout departing from the teachings of the present invention.

The temperature sensing elements are secured within a non-permeablecircular probe shoe 45 mounted in the free end of a support arm 46 whichis similarly constructed of a non-permeable material such as aluminum,plastic or the like. The support arm, in turn, is secured to the mainmachine frame (not shown) by means of a locating pin 47 so as toposition the probe shoe adjacent to but in non-contiguous relation withthe outer surface of the heated pressure fuser roll 50. A cut out 51 isprovided in the back side of the support arm, that is, the side of thearm opposed to the fuser roll, to receive an annular magnet 52. As shownin FIG. 4, the magnet is preferably circular in shape, being approximatein shape with the probe shoe and having a clear aperture 53 runningthrough the center thereof. The magnet is divided into two discretehalves along its vertical center line and is provided with two detentsnapes 53 by which the two halves of the magnet can be convenientlyjoined together. Each half of the magnet is made up of a series of northand south pole pieces with opposite pole pieces being located adjacentto each other in the manner illustrated so that a relatively strong andcontinuous flux field is established about the magnetic structure.

In assembly, the two magnet segments are snapped together over a supportshaft 55 extending outwardly from the lower portion of the support arm.The strong magnetic force field is thus passed through the nonpermeablesupport arm and probe shoe into the air gap region between the probeshoe and the fuser roll surface. A magnetic medium 56, having arelatively high coefficient of thermal conductivity, is placed in themagnetic flux field within the air gap region. Preferably a magneticfluid consisting ofa fluidic silicone based oil containing ferrite orpermeable particles which are coated with a non-coagulating material toprevent the particles from forming clusters within the fluid is hereinemployed. Such magnetic fluids are commerically available through theFerro Fluidics Corp. of Bulington, Mass. It should be clear to oneskilled in the art that the magnetic medium need not necessarily be in atruly fluidic form and the medium can be established in the mannerherein disclosed by using permeable particles, such as ferrite or thelike, which are coated with a low surface energy material such assilicone.

As can be seen in FIG. 3, the magnetic fluid is held within the fluxfield created in the air gap region and thus provides a floatinginterface between the probe shoe and the fuser roll surface whichexhibits both an extremely low thermal contact resistance and lowfricitional characteristics to the roll surface while at the same timeis capable of delivering an extremely efficient and fast thermalresponse to the sensing probe. It should also be further noted that thefloating interface, because of its fluid-like characteristics, alsoprovides a self-compensating structure capable of accommodating anychanges in the air gap size caused by fuser roll runout or otherimperfections or irregularities found on the roll surface. Similarly,the free floating heat transfer medium insures a positive, highlyefficient, flow of energy between the two bodies regardless of the shapeor roughness of the bodies or the area of the flow zone involved.Furthermore, by selecting a magnetic fluid having a low surface energy,the probe is also provided with an inherent self-cleaning feature. Anyforeign matter or toner material accumulated on the roll surface willthus pass through the magnetic fluid without being entrapped in thefluid thereby keeping the probe relatively clean under normal operatingconditions. Since the probe and the fuser roll surface are maintained atthe same temperature, there is no viscosity gradient presented to theforeign matter carried on the roll surface which would tend to draw thisforeign matter to the probe shoe surface.

As illustrated in FIG. I, the power input to the fusing system isprovided by means of an elongated radient heat lamp 60 mounted in closeproximity to the lower fuser roll surface 50 just downstream from thepoint where the roll surface enters the fuser nip. Power to the radientlamp is supplied by means of a variable power supply 61 via line 62. Inpractice, the sensing elements 40 and 41 mounted within the probe arearranged to send a voltage signal via line 66 to a comparator network63, the amplitude of which varies as the surface temperature of the rollvaries. It should be clear, however, that a current sensing network canbe used equally as well in the present system without departing from theteachings of the present invention. The comparator network basicallyconsists of a voltage comparator circuit which is arranged to comparethe voltage information received from the probe to a predeterminedreference voltage. When the compared voltage moves to either side of thereference voltage, a signal is sent via line 65 to the variable powersupply of the fuser system which, in response thereto, charges the poweroutput so as to hold the fuser roll surface temperature within apredetermined operating range.

While this invention has been described with reference to the structureherein disclosed, it is not confined to the details as set forth, andthis application is intended to cover any modifications or changes asmay come within the scope of the following claims.

What is claimed is:

l. A fuser control device for regulating the surface temperature of aheated fuser roll including means to heat the fuser roll,

a temperature sensing probe positioned in close noncontiguous relationwith the fuser roll surface whereby an air gap is formed therebetween.

magnetic means being arranged to establish a force field within said airgap,

a magnetic fluid located in said air gap and supported within the forcefield, said fluid having a relatively high coefficient of conductivitywhereby heat energy at the roll surface is rapidly and efficientlytransferred to said temperature sensing probe,

control means responsive to said temperature sensing probe beingoperatively connected to said means to heat said fuser roll formaintaining said fuser roll surface temperature at a predeterminedlevel,

wherein the magnetic fluid has a lower surface energy than the surfaceenergy of said fuser roll and wherein the size of the air gap is greaterthan the size of the magnetic fluid particles.

2. The apparatus of claim 1 wherein said temperature sensing probe isformed of a non-permeable material and said magnetic means is mountedbehind said probe in relation to the surface of said roll and arrangedto direct a force field into the air gap.

3. The apparatus of claim 1 wherein said magnetic structure is made upof a series of magnetic poles of opposite polarity with each oppositepole being mounted adjacent to the other.

4. The apparatus of claim 1 wherein the magnetic structure is formed asan annular ring.

1. A fuser control device for regulating the surface temperature of aheated fuser roll including means to heat the fuser roll, a temperaturesensing probe positioned in close non-contiguous relation with the fuserroll surface whereby an air gap is formed therebetween, magnetic meansbeing arranged to establish a force field within said air gap, amagnetic fluid located in said air gap and supported within the forcefield, said fluid having a relatively high coefficient of conductivitywhereby heat energy at the roll surface is rapidly and efficientlytransferred to said temperature sensing probe, control means responsiveto said temperature sensing probe being operatively connected to saidmeans to heat said fuser roll for maintaining said fuser roll surfacetemperature at a predetermined level, wherein the magnetic fluid has alower surface energy than the surface energy of said fuser roll andwherein the size of the air gap is greater than the size of the magneticfluid particles.
 2. The apparatus of claim 1 wherein said temperaturesensing probe is formed of a non-permeable material and said magneticmeans is mounted behind said probe in relation to the surface of saidroll and arranged to direct a force field into the air gap.
 3. Theapparatus of claim 1 wherein said magnetic structure is made up of aseries of magnetic poles of opposite polarity with each opposite polebeing mounted adjacent to the other.
 4. The apparatus of claim 1 whereinthe magnetic structure is formed as an annular ring.